1. Field of the Invention
This invention relates to a switching type bandgap controller.
More specifically, but not exclusively, the invention relates to a self-powered electronic circuit for regulating a stable reference voltage, which circuit comprises a band-gap generator to produce said stable reference voltage, comprises a system circuit block supplied by a controlled voltage obtained from said reference voltage through a comparator and an error amplifier to output a regulated voltage, and comprises a regulating loop inserted between said output and the output of the band-gap generator and including a normalizer block.
The invention also relates to a regulating method implemented by said electronic circuit.
More particularly though not exclusively, the invention relates to a voltage regulator for automotive applications, and the following description will cover this application field for convenience of illustration.
2. Description of the Related Art
As it is well known in this field, electronic regulating systems for generating stabilized voltage references are usually supplied by a voltage deriving from an external source.
For instance in the technology of electronic microcircuits, a so-called band-gap regulating system is often used which is intended to generate a stable voltage reference from a usually pre-stabilized dedicated supply line.
For example, let""s consider a first prior art solution disclosed in the U.S. Pat. No. 4,388,586 relating to a voltage regulator for an automotive alternator. This voltage regulator is provided with a precision reference voltage source 28 of the band-gap type.
The alternator output voltage 26 is compared with the band-gap reference voltage inside the comparator 44. The reference voltage source 28 is an independent block.
The German patent No. DE 196 20 181 C relates to a circuit block for producing a reference output voltage Vout. The circuit block determines an absolute voltage value Vr(To), set for a specific temperature value, and a temperature coefficient Tc=dVr/dT that is constant in specific working temperature range. The reference output voltage is obtained from these two values.
Another known solution is disclosed in the EP application No. 0751451 concerning a reference voltage regulator having a double slope temperature characteristic. The reference voltage is produced using a couple of voltage references VrA, VrB each having a predetermined temperature behavior.
A further prior art solution is disclosed in the U.S. Pat. No. 5,963,082 concerning a circuit arrangement for producing a D.C. current. An output current having a negative voltage coefficient is produced on the output terminal 27. This output current is obtained by a final mirroring of a current flowing through the resistor 17 and by a mirror circuit portion including the circuit components 24, 25, 28 and 29.
All the above prior art solutions work with voltages or currents that are just variable in temperature, but not variable in time.
Now, for a better understanding of the invention, we will examine hereinafter the problem of controlling an automotive alternator by a regulated voltage. However, differently from the above cited prior art solutions, the invention doesn""t relate to the generation of a voltage ramp for controlling a PWM signal.
In FIG. 1 of the accompanying drawings, a block diagram (A) is shown that provides an example of how a reference voltage signal Vr is generated. The reference voltage signal Vr, also known as the set-point signal, is generated by a Band-Gap block 11 connected to a supply line 5. A regulator loop circuit 1 produces an output signal Vsense=kxc2x7Vr. Therefore, the voltage signal Vr is the xe2x80x9cset pointxe2x80x9d signal for the regulator loop 1.
The signal SENSE at the output node OUT represents the variable to be controlled, that is the output signal of a system block 2 which may be for example a drive circuit portion of an alternator. This signal SENSE, following to a normalizing phase inside a block 3 placed in a feedback loop, is compared with the reference voltage signal Vr by a comparator 6 to obtain a modified reference voltage that is amplified by an amplifier block 4, in order to generate a control voltage of the system block 2.
The regulator loop, specifically the normalizing block 3, functions to make the value of the signal SENSE K times greater than the reference signal Vr, that is: Vsense=kxc2x7Vr.
Usually, the signals involved in the loop regulator circuit 1 are translated into voltage signals using small amounts of electric power.
The supply line, designated at 5 in the scheme of FIG. 1 is not always stabilized. In fact, in some applications as the ones of the voltage regulators for automotive alternators, the supply voltage on the line 5 may show negative pulses of considerable depth and duration, as shows the diagram of FIG. 2.
The ordinate of this diagram is the output voltage VGO (Voltage Generator Output) of an automotive alternator, which also represents the supply to the regulator circuit 1 on the line 5. The controlled signal SENSE is represented by the battery voltage of the vehicle. It can be understood that, since the average voltage of the controlled signal is of 14.5V and the fast surges of about 15V, the minimum voltage on the supply line 5 may drop to zero volt and below.
Heretofore, it has been trying to solve surge situations, as the ones shown in FIG. 2, by setting a lower voltage limit, under which the designer of the alternator or, more generally, of the supply line should not go.
Alternatively, a regulator circuit of hybrid structure, that is of the type comprising a monolithically integrated portion and a discrete component portion, could be used. This alternative solution allows to solve the surge problem, since the hybrid technology provides for sufficient capacitance values to counterbalance the voltage drops. However, the same structure available in hybrid form is obviously not proposable in a totally integrated form, since the capacitances of the required value can practically not be integrated.
Although in many ways advantageous and currently used for several applications, the above-discussed technical solutions tend to be economically disadvantageous, from both standpoints of electric power consumption and technical complexity.
An embodiment of this invention provides an integrated electronic circuit for regulating a stable reference voltage, which circuit has such structural, functional and consumption features such that it can be realized by a reduced number of components. Moreover, the electronic circuit is supplied by one of the voltage signals produced inside the circuit itself, thereby lowering the overall power consumption and improving the stable characteristics of the generated reference voltage signal Vr.
The electronic circuit is able to follow dynamically the system block, thus operating in a switching mode.
The electronic circuit uses as the supply voltage, the controlled signal SENSE produced by the system block itself, and applies such supply voltage to a band-gap regulator which additionally includes comparing and error amplifying means.
In other words, the band-gap circuit portion, intended to generate a stable voltage reference from the supply voltage, is to carry out the following functions:
1) generating the reference, that is the xe2x80x9cset pointxe2x80x9d signal Vr;
2) comparing the reference with a normalized controlled signal; and
3) providing an error controller function.
The features and advantages of the circuit and the method according to the invention will be apparent from the following description of embodiments thereof, given by way of non-limitative examples with reference to the accompanying drawings.